In recent years, resistance change type memories have been studied as a substitute for flash memories which are now approaching the limit of refinement and, as an example, phase-change memories have been studied vigorously using chalcogenide materials as the recording material. In a basic structure of the phase-change memory, a recording material is put between metal electrodes. The phase-change memory is a resistance, change type solid memory for storing information by utilizing that the recording material between the electrodes has different states of resistance.
The phase-change memory stores information by utilizing that the resistance value of a phase-change material such as Ge2Sb2Te5 is different between an amorphous state and a crystalline state. The resistance is high in the amorphous state and low in the crystalline state. Accordingly, reading is conducted by applying a potential difference across both ends of a device, measuring a current flowing through the device and judging whether the device is in a high resistance state or low resistance state.
In the phase-change memory, data is rewritten by changing the state of the phase-change film between the amorphous state and the crystalline state by the Joule heat generated by current. A reset operation, that is, the operation of changing the film to the amorphous state at a high resistance is conducted by flowing a relatively large current, to the phase-change film thereby melting the film and then quenching the same by rapidly decreasing the current. On the other hand, the setting operation, that is, the operation of changing the film to the crystalline state at a low resistance is conducted by flowing a relatively small current to the phase-change material and maintaining the material to a temperature higher than the temperature of crystallization. Since the volume of the phase-change material that changes the state is decreased by proceeding refinement and the necessary current is decreased, the phase-change memory is suitable to the refinement.
As a method of improving the integration degree of the phase-change memory, JP-A-2008-160004 discloses a technique of forming a plurality of through holes that pass through entire layers to a stack structure formed by alternately stacking gate electrode materials and insulating films each by plurality by corrective fabrication and depositing to fabricate a gate insulating film, a channel layer, and a phase-change film to the inner side of the through holes.
JP-A-2009-117854 discloses a technique of adding a resistance material such as TiN or C between metal electrodes and making it to act as a heater for decreasing the voltage which is necessary when the phase-change material is changed from the amorphous state to the crystalline state.
Change of the electric resistivity of the phase-change material in accordance with the temperature and the electric field intensity is explained in D. Adler et al., “Threshold Switching in Chalcogenide-Glass Thin Films”. J. Appl. Phys. 51(6), pp. 3289-3309 (1980). Specifically, in the Non-Patent Document, in the phase-change material, the electric resistance changes by several digits in the amorphous state in accordance with the temperature and the electric field. This shows that the electric resistivity in the amorphous state changes greatly depending on the constitution of a device to be measured and the current cycle voltage conditions, etc. For avoiding misunderstanding caused by the change of the electric resistivity or the electroconductivity depending on such measuring conditions, description is to be made in the present specification while showing the resistivity and the conductivity as values in the crystalline state unless otherwise specified.